BACKGROUND: The majority of deaths due to acute coronary heart disease (CHD) occur outside hospital, unexpectedly, within the first few hours following the onset of the terminal event. Data on the incidence and nature of acute pathological findings in the affected hearts as seen in routine autopsies are somewhat controversial. Detailed pathological examination of coronary arteries and myocardium of such decedents was performed to clarify the situation. METHODS AND RESULTS: Full autopsy and detailed macroscopic and microscopic examination of the coronary arteries and myocardium were performed in 170 men, all registered in the Kaunas Acute Myocardial Infarct Register, who died outside hospital of CHD within 6 hours from the onset of symptoms. Out-of-hospital coronary death was in all cases related to acute ischaemic myocardial lesions, either myocardial infarction (MI) in 92.9% of cases or patchy micronecrosis in 7.1%. In the former group, the following stages of acute infarction were found: early MI (hyperacute phase) in 48.8% of cases, definite MI (displaying grossly identifiable coagulative necrosis) in 21.8% and progressing MI (presence of signs of early MI adjacent to a healing infarction) in 22.3%. Signs of new thrombotic coronary events were found in relation to these acute ischaemic myocardial lesions in 88.8% of cases, as occlusive thrombus in 41.2%, non-occlusive, mural thrombus in 37.0% and microthrombi/microemboli in intramyocardial vessels in 10.6%. CONCLUSIONS: Out-of-hospital coronary death most commonly was related to the early or definite stages of myocardial infarction. Accurate identification of these acute ischaemic lesions was based on detailed microscopic examination of the entire ventricular myocardium, with consideration being paid to signs of cardiomyocyte involvement and early inflammatory reaction associated with it. Acute pathology of the affected coronary artery usually confirmed that these myocardial infarct lesions were the cause of the sudden out of-hospital CHD-related deaths.